The general objectives are to establish the pathways and study the enzymes involved in the biosynthesis of the diterpenoid gibberellin phytohormones and related diterpenoid substances with physiological activity. Emphasis is placed on the relationship of these reactions to other aspects of isoprenoid metabolism in the same tissue and the factors which integrate and regulate all of these reactions. Specific areas of current investigation include the following: (1) The characterization of microsomal mixed function oxidases participating in the metabolism of ent-kaurene and closely related intermediates of gibberellin biosynthesis in Echinocystis macrocarpa endosperm and Fusarium moniliforme. (2) Purification and properties of prenyl transferases from Ricinus communis (castor bean) seedlings. (3) Purification and properties of several cyclization enzymes which catalyze the conversion of the acyclic precursor geranylgeranyl-pyrophosphate to a number of polycyclic diterpenes in E. macrocarpa, R. communis and Pisum sativum preparations. (4) Studies of the subcellular localization of enzyme activities involved in diterpene biosynthesis in plant tissues. (5) Properties of fungal elicitors of synthesis of the macrocyclic diterpene phytoalexin, casbene, in R. communis seedlings. (6) A study of the chemical nature and antibiotic properties of the diterpenes induced by exposure of Zea mays seedlings to pathogenic fungi. Bibliographic references: Compartmentation of Isopentenyl Pyrophosphate Isomerase and Prenyl Transferase in Developing Castor Bean Endosperm. T. R. Green, D. T. Dennis and C. A. West, Biochem. Biophys. Res. Commun. 64, 976-982 (1975). Kaurene Synthetase from Plastids of Developing Plant Tissues. P. D. Simcox, D. T. Dennis and C. A. West, Biochem. Biophys. Res. Commun. 66, 166-172 (1975).